1) Field of the Invention
The present invention pertains generally to processing of color video signals and, in particular, to the separation of composite video signals into luminance and chrominance components.
2) Description of the Prior Art
Various techniques have been devised to increase the efficiency with which color video signals are encoded, and many such systems utilize the interrelationship between the chrominance and luminance components of the signal to achieve the desired bit rate reduction. Example of such techniques are contained in patent applications Ser. No. 826,025 and No. 826,057 filed by A. N. Netravali and C. B. Rubinstein on Aug. 19, 1977, and assigned to the same assignee as the present invention. Accordingly, the ability to effectively separate a composite video signal into chrominance and luminance components is quite important.
In prior art arrangements, separations are normally achieved with comb filters and low pass filters, as illustrated, for example, in U.S. Pat. No. 4,003,079, issued to N. Y. Woo on Jan. 11, 1977. These filters are generally "non-adaptive", and treat all areas of the picture in the same way. This leads to inaccuracies in the separation, particularly near edges in the picture, where local characteristics differ significantly from average characteristics. Further, where digital processing is involved, such filtering is accomplished by digital filters which perform a relatively large number of multiplications by general coefficients. These multipliers must be implemented by using extremely fast RAM's, thus adding to system complexity and cost.
In view of the foregoing, it is the broad object of the present invention to improve the efficiency of color signal separation by taking local picture characteristics into account. In addition, it is desired to simplify the filters used in making the separations to reduce their complexity and cost.